Synchronizing and phasing mechanisms for free piston engines



'SYNCHRONIZING AND PHASING MECHANISMS FOR FREE PISTON ENGINES Filed Oct.5, 1956 Sept. 15, 1959 J. G. MACDONALD 3 Sheets-Sheet 1 lv iw $0.. I

IN\/ E NTO R JOHN G.MACDONALD Sept. 15, 1959 i J. G. MACDONALD ,9

SYNCHRONIZING AND PHASING MECHANISMS FOR FREE PISTON ENGI NES Filed Oct.5, 1956 3 Sheets-Sheet 2 INVENTCIR JOHN G.MACDONALD Sept. 15, 1959 J. G.MACDONALD 2,904,022

SYNCHRONIZING AND PHASING MECHANISMS FOR FREE PISTON ENGINES Filed Oct.5, 1956 3 Sheets-Sheet 3 l N V E NTU R JOHN G. MACDONALD United StatesPatent SYNCHRONIZlNG AND PHASING MECHANISMS FOR FREE PISTON ENGINES JohnG. Macdonald, Goderich, Ontario, Canada Application October5, 1956,Serial No. 614,168

4 Claims. (Cl. 123-46) This invention relates to improvements ininternal combustion engines of the free piston type, and moreparticularly to improved synchronizing and phasing mechanisms therefor.

Briefly, engines of the free piston type employ a pair of opposedpistons having their inner ends reciprocating in a power or dieselcylinder and their outer ends which are of enlarged diameter operatingin enlarged compressor cylinders at the ends of the power cylinder. Onfiring the pistons are forced apart and move outwardly compressing airin bounce chambers efined between the outer ends of the pistons and theclosed ends of the compressor cylinders. At the same time, air is drawnin behind the enlarged outer ends of the pistons through suitable inletvalves into the compressor cylinders. The hot gases in the power ordiesel cylinder are exhausted as the pistons reach the outer end oftheir stroke, and these hot gases are conducted to a reservoir used tofeed a gas turbine. On exhaust of the power or diesel cylinder, theenergy stored in the compressed air in the bounce chambers serves toreturn the pistons inwardly to their firing position. The air in thecompressor cylinders is then compressed on inward movement of thepistons. Normally the compressed air is delivered to a reservoir fromwhich it is fed into the power cylinder at the completion of the nextpiston stroke to scavenge the power cylinder.

In order to maintain the opposed pistons in the same relative phaserelation, that is, in step, during their reciprocal movement asynchronizing mechanism must be provided and, in the case where two ormore cylinder units are employed, e.g. two alternately firing cylinderunits, a phasing mechanism must also be provided to keep the pistons ofthe one cylinder unit in the proper relative phase relation with thepistons in the other cylinder unit or units.

Some present synchronizing mechanisms used on this class of engine use across linkage and rocker arm between the opposed pistons. Thereciprocating mass of the rocker arms tends to cause vibration and theirmass imposes a stress on the bearings and other parts of the linkage. Inother cases, racks and pinions are used to synchronize the pistons.Since only one or two teeth of the pinion can be engaged with the rackat any given time, wear or breakage of a tooth, as in a fatigue failure,results in serious damage to the engine.

It is the object of this invention to provide a very much simplifiedsynchronizing mechanism that will overcome the problems encountered withprevious mechanisms used for this purpose.

In particular, it is the object of the invention to pro vide asynchronizing mechanism which will in addition to being simple, becompact, easily installed and adjusted, and will eliminate unbalancedstresses on the pistons and moving parts to provide vibrationless pistonsynchronism.

In the free piston engine, for high engine efficiencies, the objectiveis to add as little mass as possible to the pistons so that a highpiston velocity can be achieved and to convert a minimum of the energyimparted to the pistons on combustion into mechanical energy. It istherefore an important object to provide a synchronizing mechanism whichwill have low inertial resistance to add a minimum of mass to thepistons and to provide such a mechanism which will have low frictionallosses.

As it is desired to use the power delivered from the pistons to thesynchronizing mechanism to operate the fuel injection pump, oil pump andother accessories, it is an object to provide a synchronizing mechanismwhich will convert the high piston velocity to a low velocity in anoutput member from which the accessories can be conveniently driven.

Again it is an object to provide a synchronizing mechanism as aforesaidwhich will be strong and durable.

Another important object is to provide an extremely simple phasingmechanism for coaction with the synchronizing mechanisms of a pair ofcylinder units, e.g. a pair of alternately firing cylinder units wherebythrough the synchronizing mechanisms the pair of pistons of one cylinderunit, which are kept in correct relative phase relation by suchsynchronizing mechanisms, are also kept in correct relative phaserelation with the pair of cylinders in the other unit.

According to the invention the means of synchronizing the opposedpistons comprises a pair of rods or plungers, one non-rotatably fixed toeach of the opposed pistons and arranged in opposing coaxial relation,the ends of the rods having spiral formations of opposite hand thereonengaging a mating spiral formation on the opposite ends of anintermediate rotatable member coaxial with the rods, which member ismaintained against endwise movement while being rotated by the rods asthey reciprocate with the pistons to maintain equal rod and hence pistondisplacement. It will be appreciated that the spiral formations on theends of the rods may be either male or female and the spiral formationson the ends of the intermediate member will be the reverse.

In the preferred form of the invention, two pairs of such rods andintermediate members are employed, the rods on each piston beingdisposed in relation to provide equal stress on each piston at oppositesides thereof.

Another feature of the invention resides in utilizing the intermediaterotating member or members as the power source for the fuel injector andother engine accessories.

Still a further feature resides in forming the rod members as hollowmembers and providing for the air ex haust of these members to eliminateany air cushions which would adversely affect their reciprocation.

Further, according to the invention, the phasing mechanism is driven oh?the intermediate rotating members of the synchronizing mechanisms of apair of alternately firing cylinder units and arranged to control thefuel injection into the cylinder units, the phasing mechanism having aneutral position in which it remains during synchronism of the twocylinder units and being displaced from the neutral position on thecylinder units falling out of synchronism in a direction to increasefuel to'the lagging cylinder unit or vice versa.

These and other objects and features will become apparent from thefollowing description taken in conjunc-' tion with the accompanyingdrawings, in which:

Figure 1 is a mid-vertical sectional view, partly broken away,illustrating a free piston engine employing a synchronizing mechanismembodying the present invention;

Figure 2 is an end View, partly broken away, of the engine of Figure 1;

Figure 3 is a horizontal sectional view of the engine, partly brokenaway, showing the pistons at the opposite end of their stroke from thatshown in Figure 1; v

.Eigure 4 .is an exploded .side-elevational view on an enlarged scaleand partly broken away showing the components of the synchronizingmechanism;

' Figure '5 is an exploded perspective view on an enkrged soalegshowingthe pistons and the synchronizing mechanism "removed from the cylinderunit;

Figure -'6 is :a view similar to Figure 5, but with the pistons broken"away, showing an alternative form of synchronizing mechanism;

Figure 7 is a part-perspective, part diagrammatic view, illustrating theprinciple of a phasing mechanism accordingto the invention forcorrelating from the synchronizing' mechanisms the movement of thepistons in two separate cylinder units;

Figure 8 is a fragmentary, mid-vertical sectional detail df'analternative form of spiral drive connection between the -l'etfiprocaringrods or plungers and the intermediate driven'mem'ber of a synchronizingmechanism embodying the "invention.

With reference'to Figures 1 and 3, the cylinder unit generallydesignated at 1 is made up as in the normal construction. of free pistonengines of a central power or diesel cylinder .2, which opens at eachend to a compressor cylinder 3 which is of larger diameter than thepower cylinder, the connection between the cylinders being throughflanges 4 and 5. The compressor cylinders 3 are closed at their outerends by the walls 6, and operwithin the cylinder unit 1 are a pair ofpistons 7 having their inner ends 8 operating in the power cylinder 2 todefine therebetween a central combustion chamber 9, and having enlargedouter ends 10 operating in the compressor cylinders 3.

-As shown particularly in Figure 3, the power cylinder Zis provided witha central surrounding chamber 11 through which a suitable cooling mediummay be circulated, and additionally has a surrounding compressed airstorage chamber 12 to which communication is had from the power cylinder2, through ports 13 at the left hand end of the power cylinder, andports 14 at the right handend of the cylinder. Also leading from theright hand end of the cylinder are ports 15 in communication with anexhaust passage 16.

I :In operation, considering the starting position as illustrated inFigure 3 with the pistons 7 forced inwardly to'cornpress the gas or airin the combustion chamber 910 the ignition point, fuel is introducedinto the mixture thrmugha suitable fuel injector 17. On combustion, thepistons are forced apart in opposite directions with the outer ends .10of the pistons compressing air or gas located between these outer endsand the end walls 6 of thecompressor cylinders which define bouncechambers 18 therebetween. This compressed air forms an energy storagemedium for returning the pistons to the inner end of their stroke, asshown in Figure 3, upon the exhausting and scavenging of the powercylinder 2.

As the outwardly moving pistons 7 reach the end of their stroke, as.illustrated in .Figure 4, the right hand piston will have uncovered theports 15, allowing the escape of the hot pressure gases from the powercylinder 2 which gases are conducted away through the exhaust passage 16for operating a suitable turbine. The left hand piston, at the outer endof its stroke, uncovers the ports 13 which provide communication fromthe compressed air storage chamber 12 to the interior of the powercylinder 2, allowing compressed gases from the '12 to enter and scavengethe power cylinder. Asthe pressure in the power cylinder drops onexhausflon trf thehot gases, the energy of the compressed air in thechambers 18 will force the pistons 7 inwardly towards theposition ofFigure 3, in preparation for the next'oyol'e. During the inward movement.of these pistons the enlarged outer piston ends 10 will compress. airprwiiously admitted to the compressor cylinders 3 through inlet valves19 on the outward stroke of the pistons, and-reduced intermediateportions 20 and 2.0

4 of the left and right hand pistons define annular passages 21 and 21'which conduct this compressed air through the ports 13 and 14 to thecompressed air storage chamber 12.

It will be noted that the reduced portion 20 of the right hand piston isshorter than the left hand piston, and the inner portion 8 of the righthand piston closes the exhaust ports 15, with the pistons forcedinwardly to their firing position.

The operation of the engine thus far described isessentiallyconventional, except that the provision of the reduced intermediatepiston portions .20 and 20 eliminate the necessity of having internalvalves within the engine, as more fully discussedin my co-pending UnitedStates application Serial No. 609,579, now abandoned.

It will be understood that the means of starting the engine and thespecific fuel injector system, and other details omitted for sake ofclarity may be selected as desired.

The travel of the pistons 7 will depend to a certain extent on theirmass and inertia, and the length of the stroke will be dependent uponthe amount of fuel injected for given piston and cylinder conditions.Since there will he inherent differences in the pistons, a synchronizingmechanism must be provided to maintain the piston movement of theopposed left and right hand pistons exactly equal and opposite forengine operation. The synchronizing mechanism employed according to-oneform of the invention is best seen in Figures 1, 4 and 5. Asillustrated, attached to the inner face of the enlarged outer ends 10*of each of the pistons 7 are rods or plungers 22. Preferably, there aretwo rods attached to each piston, with the rods being disposed in"relation. These rods project inwardly of the cylinder unit parallel tothe inner piston portions 8, the inner or free ends of the rodsprojecting through suitable bushings 23 mounted in the flanges 4 of thepower cylinder 2.

The rods 22 are preferably hollow, :and are provided with ports 24affording communication between the interior of the rods and theirrespective compressor cylinders. The rods are anchored to the pistons sothat they will be secure from rotation by having their attached endsserrated as at 25, and anchored by the serrations in suitable bushings26 cast in the piston portions 10. The outer ends of the rods 22, whichoperate outside of the compressor cylinders, are provided with spiral orhelical drive formations thereon which may be either male or female. Thearrangement of the pistons and rods is such thatthe rods of the lefthand pistons are disposed coaxially with the rods of the right handpistons; that is, corresponding rods at each side of the power cylinderare coaxial.

Extending between the bushings 26 of the coaxial left and right handrods are tubular members 28 disposed, in turn, coaxially with therespective coaxial rod pair. Each of the tubular members 28 is providedwith spiral drive formations 29 and 29 to engage respectively with thespiral drive formation 27 on the ends of the left and right hand rods ofthe coaxial rod pair respectively.

It will be understood that the spiral drive formation 27 of the lefthand rods will be of opposite hand to that of the right hand rods, andtherefore, the spiral or helical drive formations 29 and 29, which willbe complementary, respectively, to the spiral drive formations of theleft and right hand rods, will also be of opposite hand.

By employing the two .sets of coaxial plungers and intermediate tubularmembers 28 on opposite sides of the power cylinder, a balanced pistonoperation will be provided by the synchronizing mechanism.

In operation, it will be understood that as the pistons reciprocate,thereby reciprocating the rods of plungers 22, these rods operating inthe tubular intermediate driven members 28 will rotate these membersthrough the engaging complementary drive formations, first in one diql ten in the opposite direction, the opposite hand of the left and righthand spiral formations providing the rotational force from the rods ofboth pistons always in the same direction.

It will be seen from Figure 1 that the rods 22 remain in telescopicengagement with the intermediate members 28, even at the outer ends oftheir strokes, and the complementary spiral or helical drive formations27 and 29 and 29', respectively, remain in engagement. Thus the rate andextent of travel of each piston is governed by the rotationaloscillation of the intermediate members 28, and as these members areheld from axial movement, the movement of the left hand piston musttherefore be precisely equal and opposite to the opposed right handpiston. While the intermediate driven members 28 are maintained againstaxial displacement during operation of the synchronizing mechanism, itmay be adjusted axially as a preset adjustment through the use of shims,as indicated at 30 to adjust the position of the pistons relative to thepower cylinder.

In operation, the inward movement of the rods 22 into the tubularmembers 28 will produce a compression of the air in these members, andthis compressed air will escape through the .ports 24 into thecompressor cylinders, so that there will be no abnormal pressures withinthe members 28 or the rods. Suitable gasket bushings 31 between thebushings 26 and the tubular members ensure against leakage of pressureair from the compression cylinders to the atmosphere, as well assupporting members 28.

It will be noted that both the tubular members 28 and the rods 22, byvirtue of being hollow, will provide a minimum of weight while aifordingstrength. Thus the synchronizing mechanism is strong and durable, whileholding the additional mass added to the pistons to a minimum, andproviding low inertial resistance.

Because of the long lead of the helical or spiral drive formations, theintermediate members 28 form relatively slow speed oscillating memberssuitable for driving the oil pump, fuel pump and other accessories, notshown. These members therefore are provided with drive pinions 32engaging suitable accessory drive gears 33. Preferably the accessorydrive is taken off both of the members 28 to maintain a balance in theload on the pistons at opposite sides of the power cylinder.

Figure 6 illustrates a modified form of the invention, in which theplungers 22' secured to the pistons 7 are hollow and have an internalspiral formation 34 adapted to cooperate with complementary spiral driveformations 35 on the ends of a coaxial intermediate shaft 36, mountedagainst axial movement in a suitable bearing 37. It will be understood,of course, that the spiral or helical formation on the left hand rod 22'will be of opposite hand to that on the right hand rod 22' andcorrespondingly on the left and right hand ends of the shaft 36. Thus,in operation, with the ends of the shaft 36 telescoped into the ends ofthe plungers 22' inward movement of the plungers will produce a rotationof the shaft 36 in one direction, and outward movement of the plungerswill produce a movement of the shaft in the opposite direction.

Again, the intermediate member of the synchronizing mechanism,comprising in this case the shaft 36, serves as a source of power foroperating the accessory equipment of the engine, and to this end, thereis mounted on the shaft 36 a pinion 38 engaging with a gear 39, drivingshaft 40, to which the accessories may be connected.

While the spiral drive formations so far described are shown as helicalrib and groove formations, anti-friction spiral drive formations mayalso be employed as illustrated in Figure 8, which is more or lessdiagrammatic. In this case, a ball bearing screw assembly is used inwhich the screw comprises a rod or plunger 41 corresponding to the rodor plunger 22, having a spiral formation 42 thereon. The intermediatedriven member 43 has at each end thereof, to cooperate with therespective plunger 41 (one plunger and one end only being shown),

a nut 44, having a spiral formation 45 formed therein. The spiralformations 42 and 45 form concave helical ball races, and the end 44 ofthe member 43 is filled with steel balls 46, and is provided with atubular ball guide 47 which interrupts the path of the balls to deflectthem from the helical race, guides them diagonally across the outside ofthe nut, and leads them back again into the raceway.

It will be understood that the actual construction of the anti-frictionspiral drive, in itself, is not new to the applicant, and is currentlymanufactured, but the application of such an anti-friction device in afree piston engine synchronizing mechanism comprises a new applicationof this principle.

It will be understood that in a free piston engine there will be thenecessity of maintaining the proper phase relation between the pistonsof difierent cylinder units where two or more cylinder units areincorporated into, the engine. The reciprocating rotational motion ofthe intermediate driven members 28'lends itself to the pro vision of asimple phasing mechanism to correlate the movement of the pistons of theseparate cylinder units as illustrated, more or less diagrammatically,in Figure 7.

In this case, it will be seen that driven from the pinions 32 of theintermediate driven members 28 of the synchronizing mechanisms of twoadjoining cylinder units, indicated as at 48 and 48' which correspond tothe cylinder, unit 1, are sector gears 49. These sector gears rockshafts 50 carrying cranks 51 connected by links 52 to a cross bar 53.Projecting from the cross bar 53 is an arm 54 on the free end of whichis journalled a control. bar 55 suitably connected in any desired mannerto con trol the fuel injection to or the compression in the bouncechambers of the two cylinder units 48 and 48'. Alternatively, the bar 55may be connected to control a combination of the fuel injection andbounce cylinder compression as will be apparent to those skilled in theart.

It will be seen that if the pistons of the cylinder units 48 and 48'have precisely the same travel and maintain their relative phase, whichwill normally be out of phase, then the rock shafts 50 Will rotateprecisely the same amount, and the left hand end of the cross bar 53will be displaced exactly the same amount as the right hand end and thecentre of the cross bar will remain stationary; that is, the arm 54 willremain stationary as will the control bar 55. However, should thepistons move out of their predetermined phase relationship, this willresult in one of the rock shafts being turned a different amount fromthe other, and one end of the cross bar 53 will be moved more than theother so that the central portion must be displaced up or down as thecase may be, moving the arm 54 and control rod 55. This movement willeffect the fuel injection into, or the compression in the bouncechambers of the cylinder units, and the control will be such as to alterthe respective control parameters in a manner to restore the desired outof phase relationship between the pistons of the two cylinder units.

It will be understood that the synchronizing and phasing mechanismsherein illustrated are by way of example only, and alterations andmodifications in the details and constructions thereof may be madewithout departing from the spirit of the invention as set forth in theappended claims.

What I claim as my invention is:

1. In an internal combustion engine a power cylinder defining centrallya combustion chamber, a compressor cylinder of greater diameter thansaid power cylinder arranged at each end of said power cylinder andhaving a closed outer end, opposed pistons having inner portionsdisposed to reciprocate in said power cylinder and enlarged outerportions disposed'to reciprocate in said compressor cylinders, and meansto provide equal and opposite synchronized movement of said pistons,said synchronized means comprising a pair of rods non-rotat- 7 ablysecuredto the enlarged outer portions of each of said-pistons. onopposite sides of the piston and project-. ing-parallet to and inthedirection of the inner portion of the piston said rods operatingthrough openings in the compressor cylinders and the rods secured to theone piston arranged coaxial with the rods of the other piston to formcoaxial rod pairs, the projecting ends of said rods having spiral driveformations thereon with the spiral drives of the rods secured to the onepiston. being of opposite hand to. the spiral drives of the rods securedto theother piston, and a rotatable driven member arranged coaxiallybetween each pair of coaxial rods and in telescopic engagement with theprojecting ends thereof, each of said driven members having spiralformations at each'end thereof complementary to. and in drivingengagement, with the spiral formations on the rod ends with which saidmembers telescopically engages whereby reciprocation of said rods onpiston reciprocation prodnce's arotational oscillation of said drivenmembers, said driven members being independently axially adjustable, andmeans maintaining said driven members in axially adjusted positionsagainst movement axially of said rods. 2, In an internal combustionengine of the free piston type having a pair of opposed pistons mountedfor reciprocation towards and from each other in a power cylinder,synchronizing means to provide" equal and opposite. synchronizedmovement of the pistons, said synchronizing means comprising at leastone pair of opposite rods, one rod of pair being non-rotatably' fixed toone of said pistons and the other rod beingnon-rotatab1y fixed.totheother piston, said rods being co-axial and adapted tomove'axia'll-y towardsland from each other on piston reciprocation, saidrods having spiral drive. formations on their adjacent ends, with thespiral formation on the end of the one rod being; of opposite hand tothe other,

and a rotatably driven member arranged. co-axially, be-v tween said rodsand in telescopic engagement with the adjacent end thereof, said drivenmember having spiral formations complementary to. and in drivingengagement with the spiral formations on the ends of said rods, wherebyreciprocation of said rodson piston reciprocation produces a rotationaloscillation of said driven member, said driven member being axiallyadjustable, and means maintaining said driven member in, adjusted axialposition against movement axially of said rods.

3, A device as claimed in claim 2 in which said rods are hollow and saidspiral rod drive formations comprise internal splines and said drivenmember comprises a shaft and said complementary driven member spiralformations comprise external splines formed on the ends of said. shaft.

4. A device as claimed in claim 2 in which said spiral drive formationsin said rods and said complementary spiral drive formations on saiddriven member are in driving engagement through a series of ballsarranged to circulate between said complementary drive formations.

References Cited in the file of this patent UNITED STATES PATENTS1,545,925 Powell July 14, 1925 2,163,767 Steiner June 27, 1939 2,453,515Kalitinsky Nov. 9, 1948 2,473,204 Huber June 14, 1949 2,578,162 WallaceDec. 11, 1951 2,800,270 Petersen July 23, 1957 OTHER REFERENCESAbandoned application of Ward, 562,248, filed Novembar 6, 1944.

